Mobile wireless communication of analog voice signals was initially carried by half duplex radio systems. Citizens Band radio, one type of mobile wireless radio, uses amplitude modulation (AM) upon a carrier frequency to transmit or receive voice signals in a half duplex manner. Other mobile wireless radios used frequency modulation (FM) within a given carrier frequency range in order to transmit or receive voice signals, half duplex, achieving improved noise characteristics. These mobile wireless radios allowed a user to move within a given radius of antennas.
A disadvantage attributable to these systems was that once a user was beyond a certain range of a given base antenna, the radio channel for a given carrier frequency was inoperative. Another disadvantage was that wireless half duplex voice communication was unacceptable to most consumers. The consumer wanted a wireless duplex voice communication system similar to his or her wired home telephone.
In the 1980's, mobile wireless duplex voice communication using an analog FM based cellular radio was introduced into the marketplace. This analog cellular system for mobile wireless duplex voice transmission was called "Advanced Mobile Phone Service" (AMPS). Introduced by AT&T, the AMPS cellular network uses the FCC assigned carrier frequency range of 800 to 900 MHz. AMPS automobile cellular units were first permanently attached to the user's car. Automobile cellular units transmitted voice signals to a cellular base station within a given cell using one watt of power. Hand-held cellular units using battery power supplies were later introduced and transmitted voice signals to a cellular base station within a given cell using one quarter watt of transmit power. Because hand held cellular units operated from a battery power supply, the power consumed by the cellular phones became critical. When a cellular phone is powered on and waiting to receive a phone call, it is in a stand-by mode consuming less power than in an active mode. However, when the hand held unit is in a stand-by mode, it constantly listens for its registration number in order to become active and receive a phone call. The stand-by mode, although lower in power than the active communication mode, continuously uses a considerable amount of power. It is desirable to further decrease the amount of power used in the stand-by mode in order to further increase the time the cellular unit requires for recharging or replacing batteries.
The human analog voice was the signal that the AMPS system was first designed to communicate. The AMPS system was optimized for carrying as many analog voice signals within a given bandwidth of a channel as possible. Mobility of the cellular telephone using low power mobile units, FM modulation, and the higher carrier frequency range (800 MHz-900 MHz) is achieved through a cellular arrangement of antennas whereby a user's signal is handed off to the next cell site as he or she moves into a different cell area. This cellular handoff can cause a temporary loss in transmission or reception. However, temporarily losing a voice signal is not critical because a user knows when there is a signal loss and can retransmit the voice information. However, signal loss, even though temporary, poses special problems for transmission of digital data. Some other AMPS mobile cellular problems causing a loss in a voice signal are fading signal strength, reflections, Rayleigh fading, and cellular dead spots.
The availability of portable computers naturally led to the desire to transmit digital data via wireless from a remote location. Presently, the AMPS voice cellular system is being used to transmit digital data in the form of Circuit Switched Cellular Data across AMPS carrier channels. Raw (baseband) digital data is converted so that it can be transmitted and received across the analog AMPS system. One disadvantage to using the AMPS system is that a narrow channel bandwidth and errors in transmission limit the baud rate of transmitting and receiving digital data. Another disadvantage of using AMPS to communicate digital data is that movement of the subscriber unit may cause a cellular handoff to occur, thus causing a loss of the digitally transmitted or received information. Loss of digital data may corrupt a data file such that it is useless. Other losses of the raw digital data may be caused by other problems of the AMPS mobile cellular system.
Another wireless communication device is a pager. Most pagers use simplex or one way communication receiving only a limited amount of information such as a telephone number. Most pagers display only information to a user on demand and perform no other function. Because only one way communication is required, an acknowledgement is not returned by the pager to the original sender. In many cases it is desirable that a sending party receive an acknowledgement minimally, telling him or her that their page message was received. In some cases it may be appropriate to respond by leaving a return page message.
A disadvantage of present paging systems is that acknowledgment and return pages are not widely available because simplex paging is more commercialized than other paging modes. Another disadvantage of present pagers is that a displayed telephone number is not automatically and electronically dialed directly on a telephone. A user reads the telephone number from a pager's display and manually dials the number on a telephone in order to contact the paging party. It is desirable for a wireless pager to have the capability of automatically dialing a received telephone number on a wireless cellular telephone via electronic means, thus integrating the features of a wireless cellular telephone with that of a duplex pager.
A landline-dependent system that is presently widely used is a high speed fax-modem. Fax-modem hardware and firmware in conjunction with fax and data communication application software have the capability of sending digital data over various modem protocols as well as sending facsimile data by using the various facsimile protocols. Fax or data communication application software may operate on different hardware such as home or portable computer, personal communicator, personal digital assistant, or other electronic devices. Examples of modem protocols for standard modulated data are CCITT V. 22bis, CCITT V. 23, CCITT V.32, Bell103, and Bell212A. Modem protocols that include error control include CCITT V.42, MNP2, MNP3, MNP4, and MNP10. Modem protocols that provide data compression are CCITT V. 42bis and MNP5. Facsimile protocols include CCITT V.21, CCITT V.27ter, CCITT V.29, CCITT T.4, CCITT T.30, CCITT T.35, Class I-EIA/TIA 578, Class I-EIA 592, and Class II-EIA 578-SP2188. A fax-modem accepts raw (baseband) digital data from an electronic device over an internal data bus or external RS-232 port. Raw digital data is converted and modulated into data of a given protocol for transmission onto a standard telephone line. Data received from the telephone line can be converted from the modulated form into raw digital data that can be interpreted by the hardware, firmware and application software.
A disadvantage of present fax-modems is that most require a wire connection to a telephone line. Present methods of providing wireless capability for a fax-modem take the modulated analog modem output signal from a fax-modem and input this into an AMPS conversion unit. The AMPS conversion unit converts and modulates the transmitted analog modem output signal into a different analog form for transmission onto the AMPS network The analog modem output signal is converted into what is called Circuit Switched Cellular Data. Received AMPS signals can be converted from Circuit Switched Cellular Data by the AMPS conversion unit into analog modem input signals that the fax-modem can receive. Presently, fax-modems do not directly convert and modulate raw digital data into an analog signal for transmission onto the AMPS cellular network. A disadvantage of present methods of providing wireless fax-modem capability is that they require additional devices to send or receive fax and digital data over the AMPS cellular network. Another disadvantage is that more power is necessary for additional components, such as the AMPS conversion unit. Another disadvantage is that a user must carry the portable computer, fax-modem, and AMPS conversion unit to provide wireless fax-modem capability. It is desirable to incorporate a fax-modem and AMPS conversion unit into one unit providing the capability of sending Circuit Switched Cellular Data across the AMPS network.
A disadvantage of using Circuit Switched Cellular Data communication across an AMPS system is the requirement of the mobile unit to be stationary to avoid losing data from fading or cellular handoff associated with a non-stationary mobile AMPS communication. Thus, a mobile unit should avoid being moved even slightly when performing communication of Circuit Switched Cellular Data using the AMPS network.
Heretofore, providing efficient wireless transmission of both voice and data signals into one small hand held integrated package has been difficult. Furthermore, it is difficult to integrate the features of AMPS voice transmission with applications such as data transmission, electronic mail, duplex paging, as well as the provision of a Circuit Switched Cellular Data interface such as a wireless fax-modem, into a single hand held battery operated wireless unit. Further, the integration of these features into a single hand held unit has not been possible because of the unavailability of the underlying electronic components and application software required to integrate all these features into a single hand held unit. It is desirable to integrate AMPS voice communication and a data communication mode when moving between cell sites, as well as providing the capability of Circuit Switched Cellular Data Communication into one integrated hand-held unit. It is also desirable to provide a system supporting such communication to interface easily with existing AMPS systems.